GI motility + Microbiome Flashcards
Types of GI contractions. Where does each contraction take place?
Propagated : waves of contraction and relaxation; e.g. in peristalsis
Tonic: area of muscle mostly contracted in place so stimulus >> relaxation e.g. sphincters
Segmental: Movement of material back and forth e.g. in colon
Inhibited contraction: gut doesn’t move e.g. “ileus”
Name the GI tract sphincters and what they separate (hint: ULe Oddi’s Py, IV and the anals)
UES: mouth from esophagus
LES: esophagus from stomach
Sphincter of Oddi: pancreatobiliary ducts from duodenum
Ileocecal valve: small intestine from large intestine
Internal and external anal sphincters: under involuntary and voluntary control, respectively
Describe the excitation contraction coupling process in the gut (what happens at rest vs when muscle is stimulated)?
What are the 3 things that control the transmission of slow waves and how do they work? (hint: one = within interstitial cells of Cajal, the other 2 are neurotransmitters)
@ rest: slow waves = baseline membrane potentials; bring membrane potential closer to AP threshold and control frequency and timing of APs
stimulated: increased Ca2+ concentration; AP occurs on top of BER, muscle is contracted
Gap junctions, ACh, NE
Gap junctions (in interstitial cells of Cajal): allow rapid AP transmission (and concerted muscle contraction)
ACh: stimulatory; increases slow wave amplitude
NorEpinephrine: inhibitory; decreases slow wave amplitude
Describe the difference between primary and secondary peristaltic waves. (what stimulates either and what does that mean for the movement of the food bolus?)
Primary peristaltic wave: stimulated by deglutition (food moved down the esophagus but not competely)
Secondary peristaltic wave: stimulated by local esophageal distension (stretch receptors in esophageal lining stimulated by presence of food bolus>>local reflex = distension >> moves food bolus further down esophagus)
Describe the deglutition process (i.e. swallowing). (What are the 3 phases? In which phase do the UES and LES’s relax? What process propels the food bolus down the esophagus?)
Phases: Voluntray/Oral ; Pharyngeal ; Esophageal
Voluntary phase: tongue senses food >> signal received by swallowign ctr in medulla >> tongue pushes food posterior pharynx
Pharyngeal phase: epiglottis folds over trachea to cover it>> upper ES relaxes (lower ES relaxes at beginning of swallowing) >> food bolus moves down esophagus
Esophageal phase: food bolus propelled down esophagus by peristalsis
What type of muscle makes up the proximal and distal esophagus? What are each portions innervated by and what is the effect of this innervation?
Proximal esophagus has striated muscle
Distal esophagus has smooth muscle (circular and longitudinal)
Proximal esophagus innervated by vagal motor neurons w/ cell bodies in nucleus ambiguus; effect = relaxation of upper esophageal sphincter
Distal esophagus innerated by vagal preganglionic neurons w/ cell bodies in distal motor nucleus; effect = relaxation of circular smooth muscle in LES
What is the contribution of the migrating motor complex to gastric motility? What are the phases of the MMC and what hormone stimulates this process? Where is this hormone released and what influences its activity?
MMC stimulates gastric motility during fasting to remove residual food in the gut
Phases:
1: Physiologic ileus - no contraction
2: Intermittent motor activity - some contraction
3: Regular, intense and repetitive contractions
(increased Motilin levels right before Phase 3)
Motilin (secreted by M cells) stimulates this process. Released in the stomach and inhibited by eating
Which area of the stomach has phasic or tonic muscle? Why is this difference necessary for the stomach’s function? (i.e. what’s the difference in their function?)
What is the significance of the pacemaker region in the stomach in stomach contraction? Where is this region?
Fundus and part of the body (upper stomach) - has tonic muscle
Tonic muscle allows for relaxation and distension of the stomach when food enters
Lower portion of the stomach body, antrum, pylorus (lower stomach) - has phasic muscle
When stomach distended, phasic muscle pushes food down the antrum and into the pylorus
The pacemaker region is where the peristaltic waves that push food down the stomach begin and move distally (located in the body of the stomach)
Describe receptive relaxation in the stomach
Swallowing food>> vagus stimulated >> stomach distension >> filling (increases pressure) >> contraction of proximal stomach
What is the contribution of trituration to gastric emptying? Where does this process take place? Over time, what is the rate of emptying of liquids, solids and semi solids (draw a graph to illustrate this)?
Trituration breaks down large particles into smaller substances> Makes is emptying easier and faster
Liquids empty faster than semi solids which empty faster than solids
What changes occur in the duodenum when stomach emptying begins?
Food in duodenum prompts two pathways:
Duodenal cells secrete enterogastrones (Secretin, CCK,GIP) >> slow gastric emptying (slow contraction rate)
Chemoreceptors and stretch receptors activated >> activate enetric neurons to slow gastric emptying (via short reflex); activate CNS >> increases sympathetic activity/decreased parasympathetic activity (via long reflex)
What are the differences in BER and food storage between the stomach and the small intestine?
In stomach: BER = lower half of body going downwards; in small intestine, throughout but faster in the proximal small intestine
Food storage: only in stomach and colon; not in small intestine or esophagus
Contrast the following properties between the small instestine and the large intestine:
Presence of MMC
Retrograde movement
Presence of longitudinal ms
Mass movement of contents
T/F: The BER in the colon facilitates net movement of chyme (i.e. movement of chyme in one direction)
Describe the following contractile patterns:
Mixing
Haustral migration
Mass movement
Falsehood. BER doesn’t facilitate movement of chyme in one direction (there’s a back and forth movement of chyme instead)
Mixing: moves contents short distances in either direction (like segmented contractions)
Haustral migrations: move contents larger distances in either direction
Mass movement: propel contents (by like 20cm or something; happens unidirectionally, after you’ve eaten)
Briefly describe the process leading up to defacation (i.e. what’s the pathway/what reflexes control this process)
Explain how an infection from some part of the body can promote inflammation in patients with inflammatory bowel disease
Infection (disrupts mucosal barrier) >> + T cell proliferation >> + T cell migration to gut >> Inflammatory response induced
Describe the role of gut bacteria in the generation of bile acids
Some bacteria express 7 alpha hydroxylase or bile salt hydrolases that convert primary bile acids to secondary bile acids
